In the available art related to calibration systems, one kind of errors (that should be calibrated for) is caused by code group delay.
Indeed, code phase (also known as pseudo-range) measurements are now commonly processed successfully in GPS receivers to provide high accuracy position, velocity and time measurements, e. g. in differential and surveying applications. Numerous error sources in these measurements have been revealed and techniques have been developed to minimize or completely eliminate these errors. The U.S. Pat. No. 5,526,291, issued to Lennen, discloses how to solve the error in code and carrier phase caused by different receiver designs reacting differently to the same satellite signal because the different receiver types use different filtering, amplification and other components. Lennen et al. in the U.S. Pat. No. 5,515,057, describes how errors in the code and carrier phase measurement caused by electrical asymmetries in the antenna element could be solved.
One important kind of the code phase error is caused by the group delay characteristics within a GPS/GLONASS receiver. The group delay code phase errors caused by variations in the group delay across the received bandwidth are due to the specific characteristics of filters, amplifiers and other active components in a GPS/GLONASS receiver design. For instance, it is desirable for a GPS/GLONASS receiver to include the specific filter and amplifier components that would allow for the substantial filtering of out of band signals to prevent possible jamming. The code phase errors caused by the group delay characteristics within a satellite receiver are more pronounced in a GLONASS receiver than in a GPS receiver.
The technique that would allow the satellite receiver to maintain the active components with the specific desirable characteristics (like antijamming capabilities) while allowing the group delay code phase errors to be removed as an error source from the pseudo range measurements was disclosed by Gary Lennen in the U.S. Pat. No. 5,949,372, entitled "Signal Injection for Calibration of Pseudo-Range Errors in Satellite Positioning System Receivers". The '372 patent is specifically referred to in the present patent application and is incorporated herein in its entirety.
However, the Calibration Signal Generator disclosed in the '372 patent is an independently important circuit. Indeed, the Calibration Signal Generator can be used in a number of different applications, where there is a need to remove the delay group errors caused by the propagation of the received signal within the Narrow Band Receiver circuit.